I. Field of the Invention
The present invention relates generally to medical instruments and, more particularly, to an endoscope.
II. Discussion of Related Art
Laparoscopic surgery has enjoyed increasing acceptance, particularly for surgery involving the abdominal cavity. In such surgery, one or more incisions are made through the patient's skin. Thereafter, various medical instruments, including endoscopes, are inserted through the incisions and into a body cavity, such as the abdominal cavity.
In order for the surgeon to see into the abdominal cavity, the surgeon typically uses an endoscope which is inserted through a cannula and into the abdominal cavity. The previously known endoscopes typically comprise an elongated tube having one or more fixed lenses. These lenses provide an optical view of the interior of the body cavity to an eyepiece or other display means accessible to the surgeon outside the body. Illumination for the endoscope is typically provided by optical fibers which extend along the length of the endoscope and form a ring around the outer periphery of the free end of the endoscope. The opposite ends of the optical fibers are connected to a light source.
These previously known endoscopes, however, have all suffered from a number of disadvantages. Perhaps the most significant disadvantage of these previously known endoscopes is that, since the optical lenses are fixed within the endoscope, the field of magnification for the endoscope remains constant. Typically, these previously known endoscopes utilize lenses which provide low or macroscopic magnification (hereafter collectively referred to as macroscopic magnification) within the body cavity so that a relatively wide field of view of the body cavity is obtained.
In many situations, however, it would be desirable for the endoscope to provide microscopic magnification of organs contained within the body cavity. For example, in certain situations where cancerous growths within body organs are suspected, the macroscopic magnification provided by the previously known endoscopes is insufficient to examine the organ tissue in sufficient detail to determine whether the tissue abnormality is cancerous or benign. As a result, it has been necessary for the surgeon to remove the tissue to perform a biopsy and, in many cases, to remove the entire organ for subsequent pathological examination outside the body.
The removal of biological tissue from the body and subsequent pathological examination outside the body suffers from two important disadvantages. First, in the event that the organ abnormality is benign, the biopsy and possible removal of the entire organ from the body results in unnecessary harm and even loss of organ function to the patient. Second, since the subsequent pathological examination of the body tissue oftentimes occurs long after the end of the operation, in the event that the pathological examination reveals a cancerous growth within the body tissue, it is oftentimes necessary for the surgeon to re-enter the body cavity and remove additional body tissue in an attempt to completely eradicate the cancer. This disadvantageously, however, subjects the patient to a second operation.
An additional disadvantage of previously known endoscopes is that the illumination and viewing paths are separate and each path uses only a portion of the available diameter of the endoscope. It would be desirable to use the entire available diameter of the endoscope for the viewing path as it would permit the use of optical lenses with larger apertures, thus providing increased resolution in the optical image formed by the lenses without requiring an increase in the overall diameter of the endoscope.